Project Summary: Goal: Our goal is to determine the role of the host microbiome in providing resistance or enhancing susceptibility to allergic diseases. Our hypothesis is that alterations in the gut microbiome caused during early education of the immune system can affect the risk of allergic sensitization due either to shifts in microbiome composition after antibiotic exposure or to exposure to specific enteric pathogens. We also expect that certain commensal microbes/microbiomes are protective and may provide an evidence-based intervention strategy. Preliminary data: We have collected fecal microbiota samples from children in an ongoing prospective longitudinal study of offspring of individuals in the Isle of Wight (IOW) 1989 birth cohort, 30?40% of whom have allergy. We have exciting data in a small sample of infants ? 1 year old, where gut Enterobacteriaceae, primarily Escherichia/Shigella and Klebsiella, were robustly shown to be the predominant bacterial group associated with eczema; eczemic children often later develop asthma. Also, Bacteroidaceae predominance was associated with protection against eczema. In other work, we have shown that a human gut microbiota delivered as a fecal transplant can shift the immune response of C57BL/6 mice to an enteric pathogen from a Th1/17 bias to an autoimmune Th2 bias. Proposed work: We propose to create murine models of microbiome-related allergic sensitization by colonizing C57BL/6 mice with gut microbiota from IOW infants of known allergic status and testing development of bronchial hyper-responsiveness of the mice after challenge with a known human allergen. The results can then be compared to observed clinical outcomes in the IOW cohort infants. Once developed, these murine models can be used in future studies to determine gut microbiome-mediated mechanisms underlying risk of and protection from allergic sensitization, for example, by using data from IOW microbiome samples to identify particular bacteria associated with allergy, to isolate them and verify their identities using standard microbiological methods, and to study mechanisms leading to their effects on allergic sensitization in mice. Expected results: We expect to determine the ability of the gut microbiome to mediate allergic responses or protection in the Hu-microbiota mouse models and as a ?proof-of-concept? for use of the models to study this process in humans. An additional strength of these studies is that the clinical relevance of findings in the mice can be assessed in light of epidemiologic and microbiome data obtained in the IOW study. Impact and significance: We expect to provide new animal models for investigation of allergic diseases and protection from allergy as well as to identify potential new strategies to prevent initiation of allergies. Because both pathogenic and protective responses by microbiome members could be explored in these models, the results will pave the way for determining which members of the gut microbiome are major influences on the development of allergic disease and thus are targets that can be manipulated to prevent allergy.